It may sound convenient but do you have complete trust in these apps without reservation now and forever?  Not me.

Even the most reputable software are known to have security flaws or, at least, vulnerabilities.  It's a cat and mouse game of whether the good guys discover them first and have the developers patched those up before the vulnerabilities get exploited by the bad guys.

Professionals who care about privacy (journalists come to mind) do not save their most valuable account details in these password managers.  There is definitely a use case for password managers but I just wouldn't use it on something as important as tax preparation software/account that could provide access to client details.

If there is one password I remember, the one for tax preparation would be it.

Just my two cents' that's worth much less, as usual.